Conventionally, in an ultrasonic diagnostic apparatus, a focusing technique has been used for using a plurality of arrayed transducer elements at the same time and focusing a beam. The configuration of such a conventional ultrasonic diagnostic apparatus will be described below. FIG. 11 shows a block diagram of a conventional linear scanning ultrasonic diagnostic apparatus (conventional example 1).
In FIG. 11, a probe 1 is an ultrasonic probe in which transducer elements 2-1 to 2-128 are arrayed. High voltage switches 3-1 to 3-64 are switches to select the apertures to be used. A transmission pulse generator 4 is a unit for generating a transmission pulse. A cross point switch 6 is a switch for re-arranging received signals. A/D converters 8-1 to 8-64 are units for converting analog received signals into digital signals. A beam former 9 is a unit for delaying and adding the data after the digital conversions. A B-mode signal processing circuit 10 is a unit for carrying out a signal process for a B-mode displaying. A Doppler blood flow meter signal processing circuit 11 is a unit for carrying out a signal process for a Doppler blood flow meter. A color flow signal processing circuit 12 is a unit for carrying out a signal process for a color flow. An image synthesizer 13 is a unit for synthesizing the signals from the respective signal processing circuits of the B-mode signal processing circuit 10 to the color flow signal processing circuit 12 and constituting a display image. A display 14 is a unit for displaying the synthesized image. A controller 15 is a unit for controlling the respective units of the ultrasonic diagnostic apparatus. An operating unit 16 is an inputting unit that is operated by an operator. Since the operations of the ultrasonic diagnostic apparatus configured in this way are well known, their explanations are omitted.
The ultrasonic diagnostic apparatus using the arrayed transducer elements needs to process the signals from the plurality of transducer elements at the same time, and consequently needs the A/D converters whose number is equal to the number of the transducer elements used at the same time, and the beam former for receiving the digitized signals and then carrying out the delaying and adding process. Thus, this has a problem that many devices are needed. In order to solve this, a method disclosed in Japanese Laid Open Utility Model Patent Application (JP-A-Showa, 58-70208) is proposed. This method will be described below by using FIG. 12 and FIG. 13.
FIG. 12 is a block diagram of the ultrasonic diagnostic apparatus (a conventional example 2) disclosed in Japanese Laid Open Utility Model Patent Application (JP-A-Showa, 58-70208). In FIG. 12, a probe 1 is an ultrasonic probe that includes arrayed transducer elements 2-1 to 2-128. High voltage switches 3-1 to 3-64 are switches to select the apertures to be used. A transmission pulse generator 4 is a unit for generating a transmission pulse. Voltage-current converting amplifiers 5-1 to 64 are units for converting voltages into currents. A cross point switch 6 is a switch for re-arranging received signals. Current-voltage converting amplifiers 7-1 to 32 are units for converting currents into voltages. A/D converters 8-1 to 8-32 are units for converting analog received signals into digital signals. A beam former 9 is a unit for delaying and adding the data after the digital conversion. A B-mode signal processing circuit 10 is a unit for carrying out a signal process for a B-mode displaying. A Doppler blood flow meter signal processing circuit 11 is a unit for carrying out a signal process for a Doppler blood flow meter. A color flow signal processing circuit 12 is a unit for carrying out a signal process for a color flow. An image synthesizer 13 is a unit for synthesizing the signals from the respective signal processing circuits of the B-mode signal processing circuit 10 to the color flow signal processing circuit 12 and constituting a display image. A display 14 is a unit for displaying the synthesized image. A controller 15 is a unit for controlling the respective units of the ultrasonic diagnostic apparatus. An operating unit 16 is an inputting unit that is operated by an operator.
The connection of the cross point switch 6 in this conventional example 2 is shown in FIG. 13A. Numbers 1, 2, . . . are assigned to the signals in the order starting from the ends of signal receiving apertures. In the cross point switch 6, two signals adjacent to each other are connected to one output terminal. At the former stage of the cross point switch, a received signal is converted into a current. Since the two signals are connected to the one output terminal, the output to which the current of the two signals is added can be taken out from the output terminal. Hereafter, the connection of the cross point switch 6 is represented as shown in FIG. 13B. In this way, the addition of the received signals of the two transducer elements adjacent to each other enables the drops in the input numbers of the A/D converters and beam formers, which consequently enables the reduction in the device amount.
However, even the addition for every two signals as mentioned above may bring about a problem. In the signal at the aperture end, the difference between the arrival times of the signals from the transducer elements adjacent to each other is great, which makes a delay precision poor. So, in order to solve this problem, in a conventional example 3 in which the conventional example 2 is improved, the addition of the transducer elements is not uniform. This method will be described below by using FIG. 14.
FIG. 14 is the connecting method of the cross point switch in the conventional example 3. In the conventional example 3, with the approach to the center of the aperture, the number of the received signals to be added is increased, and at the end, it is assumed to be 1. The fact that the difference of the delay time is small at the center of the aperture and the difference of the delay time is large at the end is considered.
However, in the conventional ultrasonic diagnostic apparatus, even in the above-mentioned conventional example 3, depending on the convergence condition, the difference of the delay time between the transducer elements to be added becomes great, which results in the problem that the convergence precision becomes poor.